1. Field of the Invention
The present invention relates to a recording power determination method and a recording power determination device for determining a recording power for recording data on an information storage medium.
2. Description of the Related Art
Optical discs are known as information storage mediums for data recording. An optical disc apparatus irradiates an optical disc with an optical beam to record data or to reproduce data recorded on the optical disc. Even if optical discs and optical disc apparatuses are produced in the same manner, there are individual differences among the optical discs and the optical disc apparatuses. Due to the individual differences, there may occur a problem that data cannot be properly recorded on an optical disc or data recorded on an optical disc cannot be properly reproduced.
As one method for preventing such a problem, it is known to determine a recording power which is appropriate for an individual optical disc and an individual optical disc apparatus when, for example, mounting an optical disc.
FIG. 16 is a schematic view showing a general optical disc 601. As shown in FIG. 16, the optical disc 601 has a track 602 formed therein spirally. By irradiating the track 602 with an optical beam having a modified recording power, a plurality of marks and a plurality of spaces are formed on the track 602. Thus, data is recorded. The optical disc 601 includes a user data area used for data recording by the user and a recording power determination area used for determining a recording power of the optical beam. The recording power determination area is provided in an area other than the user data area (specifically, an innermost area or an outermost area of the optical disc 601).
FIG. 17 is a schematic view showing a conventional optical disc apparatus 700. The optical disc apparatus 700 includes an optical head 702, a reproduction section 704, a demodulation/ECC (Error Correcting Code) circuit 706, a recording power determination section 708, a recording power setting section 710, a laser driving circuit 712, and a recording data generation section 714.
When the optical disc 601 is mounted on the optical disc apparatus 700, the type of the optical disc 601 is identified, and the optical disc 601 is rotated. The optical head 702 has a semiconductor laser (not shown). While being rotated, the optical disc 601 is irradiated with an optical beam emitted from the semiconductor laser of the optical head 702.
For recording data on the optical disc 601, the optical head 702 irradiates the optical disc 601 with an optical beam having a predetermined recording power to form marks on the optical disc 601. In this example, data of the Run Length Limited (1,7) modulation system is recorded by a mark edge recording method. In this case, seven types of marks and spaces are formed on the optical disc 601 on the basis of reference cycle T, which is 2T at the shortest and 8T at the longest.
For reading data from the optical disc 601, the optical head 702 irradiates the optical disc 601 with an optical beam having a reproduction power which is smaller than the recording power and receives light reflected by the optical disc 601. The optical head 702 performs optical/electric conversion on the received light to generate a signal indicating the data recorded on the optical disc 601. The reproduction section 704 measures a modulation factor of the signal generated by the optical head 702, and digitizes the signal generated by the optical head 702. The modulation factor will be described later with reference to FIG. 19.
The demodulation/ECC circuit 706 demodulates the signal digitized by the reproduction section 704 and corrects errors. The recording power determination section 708 determines the recording power for recording the data based on the modulation factor measured by the reproduction section 704. The recording power setting section 710 sets the recording power determined by the recording power determination section 708 in the laser driving circuit 712. The recording data generation section 714 generates data to be recorded on the optical disc 601. The laser driving circuit 712 drives the optical head 702 to record the data generated by the recording data generation section 714 on the optical disc 601 at the recording power set by the recording power setting section 710.
FIG. 18 is a schematic view showing the reproduction section 704 in the conventional optical disc apparatus 700. As shown in FIG. 18, the reproduction section 704 includes a preamplifier 801, a sampling and holding circuit 802, an A/D converter 803, an arithmetic operator 804, and a binary data generation section 805.
The binary data generation section 805 digitizes the signal generated by the optical disc 702 to generate digitized data (binary data), and outputs a signal 705 indicating the binary data to the demodulation/ECC circuit 706 and the recording power determination section 708.
The preamplifier 801 amplifiers the signal generated by the optical head 702. The sampling and holding circuit 802 samples the signal amplified by the preamplifier 801 and holds the peak value and the bottom value of the signal. The A/D converter 803 digitizes the peak value and the bottom value held by the sampling and holding circuit 802. The arithmetic operator 804 performs an arithmetic operation on the digitized peak value and bottom value to obtain a modulation factor.
FIG. 19 is a schematic view showing a waveform of the signal which is output from the preamplifier 801. As shown in FIG. 19, the modulation factor is represented by (A−B)/A, where amplitude A is the amplitude from the signal level when no optical beam is emitted by the semiconductor laser of the optical head 702, or the signal level when no influence is exerted by the light reflected by the optical disc 601 even though the optical disc 601 is irradiated with an optical beam having a reproduction power emitted by the semiconductor laser of the optical head 702, to the signal level corresponding to the mark; and amplitude B is the amplitude from the signal level when no optical beam is emitted by the semiconductor laser of the optical head 702 to the signal level corresponding to the space.
Returning to FIG. 17, a conventional recording power determination method will be described.
On the optical disc 601, a constant parameter is recorded to be used for determination of the recording power. The optical head 702 generates a signal 703 indicating the constant parameter (hereinafter, referred to as a “predetermined value”) read from the optical disc 601, and outputs the signal 703 to the reproduction section 704. The binary data generation section 805 of the reproduction section 704 generates the binary signal 705 obtained by binarizing the signal 703 indicating the predetermined value, and outputs the signal 705 to the recording power determination section 708.
The recording power setting section 710 sets a test recording power of the optical beam in the laser driving circuit 712. The recording power setting section 710 sets eight different test recording powers A through H. In this example, the test recording power A is the largest power, and the test recording powers become smaller from the test recording power B toward the test recording power H.
The recording data generation section 714 generates test data, and outputs a signal 715 indicating the generated test data to the laser driving circuit 712. The laser driving circuit 712 drives the optical head 702 to record the test data over substantially one circle of the track continuously from a predetermined position in the recording power determination area of the optical disc 601. The recording data generation section 714 generates the test data such that the optical head 702 continuously forms 8T marks and 8T spaces on the optical disc 601. The test data is repeatedly recorded over substantially one circle of the optical disc 601 at the test recording powers A through H. FIG. 20 shows areas of the optical disc 601 corresponding to the test recording powers A through H with letters “A” through “H”.
When the recording of the test data is finished, the optical head 702 irradiates the optical disc 601 with an optical beam having a reproduction power. By this, the test data recorded on the track is read, and a signal indicating the test data is generated. The amplitude of the signal generated by the optical head 702 changes in accordance with whether or not the marks are formed on the optical disc 601. The signal 703 generated by the optical head 702 is input to the reproduction section 704.
Returning to FIG. 18, the preamplifier 801 of the reproduction section 704 amplifies the signal 703. The sampling and holding circuit 802 holds the peak value and the bottom value of the signal amplified by the preamplifier 801. The A/D converter 803 digitizes the peak value and the bottom value of the signal held by the sampling and holding circuit 802. The arithmetic operator 804 performs an arithmetic operation on the digitized peak value and bottom value to obtain the modulation factor of the signal. Since the amplitude of the signal 703 is different in accordance with the test recording powers A through H, the modulation factor is also different in accordance with the test recording powers A through H. The arithmetic operator 804 generates a signal 707 indicating the modulation factors of the signal, and outputs the signal 707 to the recording power determination section 708.
The recording power determination section 708 determines the recording power based on the modulator factors corresponding to the test recording powers A through H by one of two conventional recording power determination methods described below.
FIG. 21 shows a view for describing a first conventional recording power determination method, and is a graph illustrating the relationship between the test recording power and the modulation factor. According to the first conventional recording power determination method, the recording power determination section 708 selects a recording power P0 corresponding to a modulation factor M0 based on the correlation between the plurality of test recording powers and a plurality of modulation factors corresponding to the plurality of test recording powers. The recording power determination section 708 calculates a product of the recording power P0 and a predetermined value read from the optical disc 601 and thus determines the recording power used for recording data. The recording power determination section 708 outputs a signal 709 indicating the calculated recording power to the recording power setting section 710.
FIG. 22 shows a view for describing a second conventional recording power determination method, and is a graph illustrating the relationship between (i) the test recording power and (ii) the product of the modulation factor and the recording power. According to the second conventional recording power determination method, the recording power determination section 708 calculates a product of each of the plurality of test recording powers and a modulation factor corresponding thereto, and thus creates an approximate line indicating the correlation between (i) the test recording power and (ii) the product of the modulation factor and the test recording power. Then, the recording power determination section 708 obtains a recording power Pthr at which the product is 0 on the approximate line. Next, the recording power determination section 708 calculates a product of the recording power Pthr and a predetermined value read from the optical disc 601, and determines the recording power used for recording data. The recording power determination section 708 outputs a signal 709 indicating the calculated value to the recording power setting section 710.
However, an appropriate recording power cannot be determined either by the first conventional recording power determination method or the second conventional recording power determination method.
In the case that the recording power determination section 708 determines the recording power according to the first conventional recording power determination method, the recording power determination section 708 cannot determine an appropriate recording power when, for example, there is a relative tilt between the optical disc 601 and the optical head 702. Hereinafter, with reference to FIG. 23, the recording power when there is such a tilt will be described.
FIG. 23 is a graph illustrating the relationship between the recording power and the modulation factor. In the graph of FIG. 23, a solid line 1101 represents the result obtained when there is no tilt at the time of data recording or at the time of reading of the recorded data. A solid line 1102 represents the result obtained when there is a tilt at the time of data recording, but there is no tilt at the time of data reading. A solid line 1103 represents the result obtained when there is a tilt both at the time of data recording and at the time of data reading. The modulation factor is smaller when there is a tilt than when there is no tilt. In the case where there is no tilt at the time of data reading but there is a tilt at the time of data recording, the modulation factor corresponding to the recording power H, which is smallest among the eight recording powers, cannot be measured. Similarly, in the case where there is a tilt both at the time of data recording and at the time of data reading, the modulation factor corresponding to the recording power H cannot be measured.
Test data is recorded and read before user data is recorded. The test data is read immediately after being recorded. Accordingly, when the test data is recorded and read while there is a relative tilt, the result represented by the solid line 1103 in FIG. 23 is obtained. When determining the recording power by the first conventional recording power determination method, the recording power determination section 708 selects a recording power P1103 corresponding to the modulation factor M0. This result is influenced by the tilt at the time of test data recording and also by the tilt when the test data is read (hereinafter, referred to as “at the time of test data reading”).
In the case where there is a tilt at the time of test data recording, it is considered that there is a tilt also at the time of user data recording. However, there is not necessarily a tilt at the time of user data reading. It is very rare that the user data is read immediately after being recorded. In many cases, the user data is read by another optical disc apparatus or after the optical disc is re-mounted on the optical disc apparatus. Therefore, there is no tilt at the time of user data reading. Accordingly, for determining the recording power, only the influence of the tilt at the time of test data recording needs to be considered. It is not necessary to consider the influence of the tilt at the time of test data reading. Therefore, the recording power which should be selected when there is a relative tilt is not the recording power P1103 but is a recording power P1102 in FIG. 23. When determining the recording power by the first conventional recording power determination method, the recording power determination section 708 selects the recording power P1103, which is larger than the recording power P1102. Therefore, the optical head 702 records data with an unnecessarily large power. As a result, by the first conventional recording power determination method, the optical disc 601 is deteriorated unnecessarily quickly by repeated recording.
When using the second conventional recording power determination method for determining the recording power, the following occurs as shown in FIG. 24. When the recording power determination section 708 selects four larger test recording powers among the eight test recording powers and creates an approximate line indicating the correlation between (i) each of these four test recording powers and (ii) the product of the modulation factor and each of these four recording powers, the recording power at which the product is 0 on the approximate line is the recording power Pthr1. By contrast, when the recording power determination section 708 selects four smaller test recording powers among the eight test recording powers and creates an approximate line indicating the correlation between (i) each of these four test recording powers and (ii) the product of the modulation factor and each of these four recording powers, the recording power at which the product is 0 on the approximate line is a recording power Pthr2.
As is clear from FIG. 24, the recording power at which the product is 0 on the approximate line is significantly different in accordance with the test recording power. Namely, when determining the recording power by the second conventional recording power determination method, the recording power to be determined is significantly different depending on the test recording power which is used for recording the test data and depending on the test recording power, the result of which is used for determining the recording power. Accordingly, when using the second conventional recording power recording method, the recording power determination section 708 cannot uniquely determine an appropriate recording power. In addition, when the recording power determination section 708 determines a recording power larger than an appropriate recording power, the optical disc is deteriorated unnecessarily quickly. By contrast, when the recording power determination section 708 determines a recording power smaller than an appropriate recording power, the data cannot be recorded properly on the optical disc.
The present invention, made in light of the above-described problems, has an object of providing a recording power determination method and a recording power determination device for determining an appropriate recording power.